Electron beam writing system

Abstract

An electron beam writing system which permits a relatively low voltage to be applied to perform high speed focus correction with high accuracy. The electron beam writing system includes a focus corrector arranged inside a lens which provides the largest product of the magnification factors of the lens and all succeeding lenses and the optical path length of the lens at issue. Thus, the electron beam provides high sensitivity and a small change in the magnification ratio due to the correction.

We claim: 
     
       1. An electron beam writing system comprising: means for emitting electrons;   an optical system for causing an electron beam to be emitted from said emitted electrons, and for projecting said electron beam on a writing object, wherein said optical system has a plurality of lenses including an objective lens for focusing said electron beam on said object wherein said objective lens has two lenses; and   an electrostatic focus corrector for correcting the focus of said electron beam, wherein said focus corrector is arranged at a position in said two-lens objective lens that is closer to an object plane of the optical system than to an image plane of the optical system with respect to the objective lens.   
     
     
       2. An electron beam writing system according to claim 1, wherein the two lenses of said objective lens are electromagnetic lenses. 
     
     
       3. An electron beam writing system according to claim 2, wherein said focus corrector is arranged at one of said electromagnetic lenses which is nearer to said object plane than is the other of said electromagnetic lenses. 
     
     
       4. An optical system for an electron beam in an electron beam writing system having a plurality of lenses including an objective lens opposite to a writing object, comprising: an electrostatic focus corrector for correcting the focus of said electron beam, said focus corrector being arranged inside said objective lens;   wherein said focus corrector is arranged at a position in said objective lens that is closer to an object plane of the optical system than to an image plane of the optical system with respect to said objective lens; and   wherein said objective lens is composed of e pair of electromagnetic lenses.   
     
     
       5. An optical system according to claim 4, wherein said focus corrector is arranged at one of said pair of electromagnetic lenses which is nearer to said object plane and farther from the sample, as compared with the other of said pair of electromagnetic lenses. 
     
     
       6. A focus corrector used in an optical system for an electron beam in an electron beam writing system which has a plurality of lenses including an objective lens and serving to correct the focus of said electron beam, wherein said focus corrector is an electrostatic focus corrector, and arranged at a position in said objective lens that is closer to an object plane than to an image plane of said optical system with respect to said objective lens, and wherein said objective lens comprises a pair of electromagnetic lenses. 
     
     
       7. A focus corrector according to claim 6, wherein said focus corrector is arranged at one of said pair of electromagnetic lenses which is nearer to said object plane than is the other of said pair of electromagnetic lenses.